Before closing this section, we address whether NH\(_3\)  can be produced substantially by water-rock reactions and then emitted into the atmosphere. Hydrothermal systems on early Earth may produce NH3 from the reduction of nitrite and nitrate [1]}, [2]}. On a planet with an H2-dominated atmosphere, however, atmospheric production of the oxidized nitrogen including nitrite and nitrate should be very limited. Moreover, the storage capability of NH3 by the ocean is vast and limits the emission into the atmosphere. At the pH value of 8 (a lower pH would further favor the partitioning of NH3 in the ocean), \(10^{-6}\)  bar of atmospheric NH3 requires a dissolved ammonium concentration of \(10^{-3}\)  mol/L in equilibrium [3]}. The mass of NH\(_3\)  in the atmosphere and ocean is then \(\sim 10^{-5}\)  of the planetary mass. This would only be possible if much of the planet's rocky core begins with a volatile composition similar to carbonaceous chondrites, and most of this nitrogen is partitioned into the atmosphere and ocean as NH\(_3\)  [4]}, which is highly unlikely as N2 is thermochemically favored. Therefore, the concentration of dissolved NH3 should be small and so is the atmospheric NH3 on a planet with a massive ocean.
